Optical encoders are used to monitor the motion of, for example, a shaft such as a crankshaft. Optical encoders can monitor the motion of a shaft in terms of position and/or number of revolutions of the shaft. Optical encoders typically use a codewheel attached to the shaft to modulate light as the shaft and the codewheel rotate. The light is modulated as it passes through a track on the codewheel that includes a pattern of transparent and opaque sections. As the light is modulated in response to the rotation of the codewheel, a stream of electrical signals is generated from a photodetector array that receives the modulated light. The electrical signals are used to determine the position and/or number of revolutions of the shaft.
When using an optical encoder, the current of the electrical signals fluctuates between a “dark current” and a “light current”. The dark current corresponds to when an opaque section of the track on the codewheel is positioned between the light source and a photodetector of the photodetector array. The light current corresponds to the dark current plus current generated by a photodetector of the photodetector array when a transparent section of the track on the codewheel is positioned between the light source and a photodetector of the photodetector array. In this way, the modulated light causes the electrical signal to swing continuously from dark current to light current and back.
It may be desirable to change the frequency of the electrical signal in order to achieve a higher resolution. An interpolation integrated circuit (IC) may be used to change the frequency of the electrical signal. However, using an interpolation IC in this way may require a new PCB layout (due to the additional interpolation IC component) and package redesign. Typically, this increases the cost and size of the product. Moreover, an additional IC typically increases current consumption, which directly impacts heat dissipation and performance.